Wiring a PV array

A PV array is compoed of PV panels or modules wired together in parallel or in series, to acheive the voltage required by the inverter. Inverters come with software that can be used to compute the best configuration for your array. Parallel branches are wired together at a combiner box located close to the array, usually inside the loft space. The wiring from the combiner box is connected to a DC disconnect switch before feeding into the inverter. The AC output from the inverter is connected to an AC disconnect switch, so utility personnel can disconnect the array from the grid when necessary. The AC wiring is then wired to the houshold consumer unit.

 
Wiring differs from normal household wiring as the output from the PV array is direct current as opposed to alternating current in normal household wiring. DC wiring generally uses lower voltages, and as a result is typically thicker, in oder to limit voltage drop. It’s important to size the wires correctly based on the amperage at full load, multiply by 1.25 so that it never carries more than 80% of it’s rated current and follow the applicable wiring codes. In the u.k. the IEE wiring regulations (BS 7671). For the wiring connecting the PV array to the inverter, allow an additional safety factor of 125% for exceptionally sunny days. Follow the appropriate wiring color code. Encase wiring in conduit, in accordance with its degree of exposure.
 
PV array wiring is also susceptible to voltage drop. Voltage drop is dependant on the current flowing through the wire, the length and gauge of the wire. As voltages are lower in PV systems, we know the current flowing will be proportionatly higher (Watts = Volts x Amps), and will adversely effect voltage drop. Wiring should be sized to limit voltage drop ideally to no more than 2% in PV systems, owing to the high cost of the PV panels. You should follow appropriate tables to determine wire gauge, based on voltage drop in addition to required safety codes, and consider over sizing cables if the system may be expanded in the future, particularly where cables are difficult to access.
 
Grounding
 
There is a need for both equipment grounding and system grounding. A continuous equipment grounding wire must connect to every noncurrent carrying metal part of the system, and connect to the grounding electrode through the grounding electrode conductor. This is to prevent shock when an exposed part of the system becomes live as a result of a fault. Metal conduit can act as the grounding wire. The PV array should also be system grounded, with a grounding conductor attached to the negative wire as close to the PV panels as is practical. The array must also be fitted with DC Ground fault protection. Most inverters have built-in ground fault protection, to isolate the system ground in the event of ground fault conditions, otherwise a ground fault circuit interrupter must be wired into the system. The equipment grounding wire for the array circuit, can be as large as the current carrying conductors, but at least, no smaller than the wire rated for the overcurrent device protecting the circuit. If the current carrying wires have been oversized to reduce voltage drop, the earth wire must be oversized proportionately.
 
The grounding electrode conductor is a bare copper wire connecting the grounded conductor and / or the equipment grounding conductor, It should be sized to be a least as big as any conductor in the system

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